Control circuit



H. WEST comma, czaoum Filetfi Dec. 31, 19:57

VOL7I46E REGULATOR P W W 2 w A mm a [P a H Patented May 7, 1940 PATENT OFFICE common cmcorr Harry R. West, Pittsfleld, Mass assignor to General Electric Company, a. corporation of New York Application December 31, 1937, Serial No. 182,737

5 Claims.

This invention relates to control circuits and more particularly to improvements in holding circuits for contact making measuring instruments.

5 In many automatic control and regulating systems the primary control'device is a relatively delicate contact making measuring instrument or relay. By reason of the fact that the variable quantity to which such devices respond often have continuous, minute and rapid fluctuations, together with the fact that such instruments are often mounted on panels subject to vibration, the usual tendency is for the contacts of such instruments to chatter and make vibratory or trembling engagement. I'his causes injurious arcing and burning of the contacts and also causes undesired intermittent starting and stopping oi the controlled or regulating apparatus under the control of these contacts thereby accelerating wear on these parts and requiring excessively high maintenance expense.

Heretciore, holding coils have been associated with these contact making instruments for hold ing the contacts in firm engagement and thus preventing the above described undesired chattering action. The contacts usually are not large enough to carry directly the actuating current of the ultirn sly controlled device, such as a regulator oper motor, and it is customary to interto pose an auxiliary relay or relays between the contacts this device.

For any years it was standard practice to use holding coils in contact making voltmeters corrected in parallel or shunt with the relay coils.

space limitations prevented the winding of full voltage holding coils and therefore it was necessary to wind the-coils for about fifteen volts and use resistors to limit the current to the nroner value. this arrangement had the disad- .wing approximately ill of an amlding coll current through the contact contacts and this current when to the relay current placed a considerable the delicate contacts of the meter.

In .nn, this arrangement required the use of a relatively large resistor tube. More re cently, the holding cells have been connected in series with the relay coils. However, the relay coil takes about four times as much current in the open. (aroused out) position as it does in the closed ulled in) position. Tins means that coils receive an initial energization es the final energization' and this ization would cause the contacts nroduce unsatisfactory operation.

' In accordance with this invention, these difficulties are overcome by energizing the holding coils, or their equivalent, by transformer action; usually from the winding which acts as the main load on the meter contacts. This winding is usually the auxiliary relay winding, although in certain cases it may be a motor winding or some other winding which does not require a current large enough to injure the contacts. The eifect of this arrangement is to make the energization of the holding means independent of the inrush, starting or magnetizing current of the load on the contacts and in addition, the increase in cur-- rent through the contacts required by the holding means can be made very small, such as 15 milliamperes for example.

An object of the invention is to provide a new and improved anti-contact-chatter ,holding ar rangement for contact making instruments or primary relays.

Another object of the invention is to provide a new and improved holding coil circuit for 0011- tact making voltmeter-s.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the single figure of the accompanying drawing, there is illustrated therein diagrammatically an embodiment of the invention as applied by way of example to a contact making voltmeter l for controlling a voltage regulator 2 for an alternating current feeder circult ii. Regulator 2 may be of any suitable construction, such, for example, as an induction regulator or step regulator. The regulator is operated by a conventional reversible motor l. whose direction of operation is controlled by raise and lower contacts 5 and t on the meter. Interposed between the raise and lower contacts and the terminals of the motor are a pair of auxiliary relays or contractors 'l and is provided with a common magnetic core structure.

Holding coils ii and to are provided on the meter and they are comiected respectively to be energized by secondary windings Ill and if: as-- sociated with relays l and a respectively, that is to say, the secondary windings H and are energized by transformer action respectively from the main windings of the relays l and El.

By reason of an arrangement of limit switches it and M, which is preferred at present, the windings it and i2 are insulated from main windings of the relays although it will be oh" vious to those skilled in the art that, generally Till speaking, autotransformer connections of these windings may also be used.

The contact making voltmeters, the relays and the motor are all supplied with current from the secondary winding of a potential transformer l3 connected across the main regulated circuit.

In operation, whenever the voltage of circuit 3 departs sufliciently from a predetermined normal value, the raise contacts 5 or the lower contacts in 6 will close. This will complete a circuit for energiaing either the relay 'l or the relay 8 which will then pick up and complete an energizing circult for the motor 4 which will cause it to drive the regulator 2 in the proper direction to restore 15 the voltage to normal. .As soon as normal voltage is attained, the meter contacts will open and the parts will return to the position illustrated in the drawing.

As previously mentioned, the initial current of i each relay is much higher than the current after the relay pulls in. This is because inits dropped out position, the magnetic circuit has a relatively long air gap, resulting in a relatively low inductance and thus a relatively low reactance of 2.1 the operating winding. ,A relatively high magnetizing current is therefore drawn through the relay winding. However, as-soon as the relay picks up, the air gap is shortened, the inductance increases and the magnetizing current is reduced.

:0 These changes in current in the relay coil correspond to changes in magnetizing current of a transformer so liar as the secondary windings II and I2 are concerned, so that these changes in relay current are not reflected in the holding coil circuits. Consequently, the holding coil current is relatively steady and is determined by the impedance of the holding circuits and the voltage of the windings H and I2.

Furthermore, by selecting a proper ratio of n turns of the main relay coil to the secondary coil,

the holding circuit current can be made relatively high in the secondary circuit, although the refiection or this current in the primary or meter contact circuit will be relatively small and thus,

will not produce an objectionable burden on the relay contacts.

Each holding coil when energized attracts magnetically the pivoted contact beam of the voltmeter and holds the contacts in relatively firm 50 engagement.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those sl'illed in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a contact making instru ment, an alternating current circuit controlled by the contacts of said instrument, a load device having mechanically movable magnetic parts operated by a winding connected in said circuit, holding means for the contacts of said instrument, and means for energizing said holding means by transformer action from said winding.

2. In combination, a contact making instrument having an operating winding, an alterhating current circuit controlled by the contacts of said instrument, an electromagnetic device having a winding connected in said circuit and a secondary winding inductively related thereto, a holding coil on said instrument which is separate from said operating winding, and connections for energizing said holding coil from said secondary Winding.

3. In a control circuit, a contact making instrument connected to respond to the value of a variable quantity to be controlled, an inductive load connected to be controlled by the contacts oi! said instrument, said inductive load having a mag- 25 netic circuit whose reluctance decreases substantially after said load is energized, holding means for the contacts of said instrument, and means for energizing said holding means by transformer action from said inductanve load.

4. In a control circuit, a contact making instrument connected to respond to the value or a variable quantity to be controlled, an inductive load connected to be controlled by the contacts of said instrument, said inductive load having 9; variable air gap magnetic circuit, holding means for the contacts of said instrument, and means for energizing said holding means by transformer action from said inductive load, the ratio of said transformer action being such that the secondary holding current is larger than the corresponding primary current carried by said contacts.

5. A control system for a reversible motor operated automatic regulator comprising, in combination, a primary contact making relay, motor direction of operation controlling secondary relay means including a pair of electromagnets for operating said secondary relay means, alternating current circuits controlled by said primary relay for selectively energizing said electromagnets, holding coils on said primary relay, and secondary windings energized by transformer action respectively from said electromagnets connected respectively to energize said holding coils.

HARRY R. WEST. 

